High Speed Downlink Packet Access (HSDPA) transmissions to a User Equipment (UE) have up until now only occurred from one network node, the so-called serving, Node B. During the last couple of years the following trends have however become apparent:                UE capabilities and processing power have increased considerably. This is driven both by the development of the long-term evolution (LTE) supporting significant peak data rates and the multi-carrier (MC) evolution within Wideband Code Division Multiple Access/High Speed Packet Access (WCDMA/HSPA).        Main-remote network architectures in which multiple cells located at different physical locations share baseband unit (and which enables fast coordination without Radio Network Controller (RNC) involvement between the cells) are becoming increasingly popular.        The user demand for high peak data rates and operators' desire to manage their wireless resources efficiently have increased and continue to increase. This is a consequence of that mobile operators have started to rely on WCDMA/HSPA technology to offer mobile broadband services.        
These observations have triggered discussions in the Third Generation Partnership Project (3GPP) on standardizing support for multi-cell transmissions. One of the areas discussed concerned multi-flow transmission techniques (e.g. Single-Frequency Dual-Cell High-Speed Downlink Packet Access (SF-DC-HSDPA): This class of techniques is based on that several, independent data streams are transmitted to the same UE from different sectors possibly belonging to different sites. The gains associated with this class of techniques stems from “spatial resource pooling”.
With regard to the multi-flow transmission, the 3GPP specification group for Radio Access networks (3GPP TSG RAN) has agreed on a new work Item “Multi Point Transmission” (in short MP Transmission) or multiflow transmission. It allows for a primary and a secondary or additional High Speed (HS) serving cell to simultaneously send different data to a User Equipment UE on the same frequency or frequencies. The HS radio links can be located in the same base station or Node B (Intra Node B MP Transmission) or they can be located in two different Node Bs (Inter Node B MP Transmission). The base stations can be controlled by the same radio network controller (RNC), or by different RNCs, while there is an Iur connection between two RNCs.
The current specification does not support two HSDPA data streams transmitted on the same frequency/frequencies to the same UE.
When a HSDPA Radio Link is setup, it is setup according to normal legacy HSDPA operation supported by the current 3GPP specification, such as that defined in 3GPP TS 25.433 v11.0.0 and 3GPP TS 25.423 v11.0.0.
In MP transmission, when a UE moves to an area where another Cell with the same frequency/frequencies could be added so that HSDPA data can be transmitted in both cells to this UE, a radio network controller (RNC) needs to setup the second HSDPA Radio Link. In the control plane of the Node B Application Part (NBAP) and Radio Network Subsystem Application Part (RNSAP) NABP/RNSAP, this can be done by mostly reusing the traditional HSDPA radio link setup/addition and reconfiguration procedure.
However, there exists at least one problem. In dual cell HSDPA, the base station knows that it is in this kind operation. There is only one RLC data flow for all the carriers, the separation of data that should be transmitted in the different cells is done in the Node B.
However, in MP transmission, the two Radio Links may belong to different base stations. When the second HSDPA radio link is setup and hence the UE and the network go into MP operation, there is no means for the base station with the first Radio Link to know if it is still in normal HSDPA operation, or changed to a Multi Point Operation. This means that it is essential for base stations to know if they are in MP transmission so that they can handle the physical layer accordingly.
For example, in the case that a single High Speed-Dedicated Physical Control Channel (HS-DPCCH) is used for MP transmission for HS-DPCCH Feedback, base stations need to know that they are in MP transmission or not in order to decode the channel. The reason for this is that the UE will essentially double the feedback channel, where one half is provided for feedback to one base station and the other half for feedback to the other base station. If a base station does not know that it is operating in MP transmission, it may read the wrong feedback channel, which could be fatal.